June 1, 2010



The Global Atmosphere Watch (GAW) aerosol programme (GAW, 2007) strives "to determine the spatio-temporal distribution of aerosol properties related to climate forcing and air quality up to multidecadal time scales". The specific objective of the GAW Aerosol Lidar Observation Network (GALION) is to provide the vertical component of this distribution through advanced laser remote sensing in a network of ground-based stations. The aerosol properties to be observed include the identification of aerosol layers, profiles of optical properties with known and specified precision (backscatter and extinction coefficients at selected wavelengths, lidar ratio, Ångström coefficients), aerosol type (e.g. dust, maritime, fire smoke, urban haze), and microphysical properties (e.g., volume and surface concentrations, size distribution parameters, refractive index). Observations will be made with sufficient coverage, resolution, and accuracy to establish comprehensive aerosol climatology, to evaluate model performance, to assist and
complement space-borne observations, and to provide input to forecast models of "chemical weather".


All main long-term objectives of GAW, as stated in the WMO Global Atmospheric Watch (GAW) Strategic Plan: 2008-2015 (GAW, 2007), are related to the 4-dimensional space-time distribution of aerosols, with different demands on measurement characteristics:

  1. Detection of long-term man-made trends in the concentration of greenhouse gases and aerosols related to climate change above natural variability; (requires a long-term climatology for aerosols including the vertical distribution for identification of sources and impact on radiation as well as cloud formation)

  2. Better environmental assessments related to climate, air quality, ozone depletion and the long-range transport of pollution between regions; (aerosols in elevated layers are excellent tracers for long range transport of pollution)

  3. Better quantification of pollution sources and their atmospheric pathways to sensitive downwind receptors; (significant long-range transport occurs at elevated layers, precise arrival heights are needed to trace substances back to the source)

  4. Reliable global concentration fields of selected chemical variables and aerosols at various altitudes for the study of outstanding problems in atmospheric chemistry;(advanced profiling is needed at a number of anchor stations to support and improve space-borne observations)

  5. Better prediction of UV intensities at the Earth's surface both in populated and remote regions; (aerosols have a significant impact on UV radiation, radiative transfer calculations require the vertical distribution of constituents)

  6. Direct observation of plumes from major events such as forest fires, dust storms and volcanic eruptions; (these plumes are associated with characteristic aerosol emissions, large parts of the plumes are within elevated layers)

  7. Improved regional forecasts of both weather and air quality, and to provide forecasts in regions where these are unobtainable at the moment; (understanding transport of pollutants at elevated layers and down mixing into the boundary layer is essential for air quality forecasts, aerosols are among the most important pollutants and are excellent tracers for other components).

In view of these objectives the present observations of the vertical distribution of aerosols are far from adequate. While within GAW an observing network for aerosol properties at ground level is well established and a programme has been initiated for the coordination of sun-photometer networks (GAW, 2005) measuring column integrated aerosol optical properties, the vertical component is not yet covered. The implementation principles of the GAW strategic plan recommend filling gaps like this by "working with the GAW observational community and Contributing Partners that have substantive networks to complete the global network, and improve collaboration between National Hydrological and Meteorological Services, environmental agencies and research organizations in filling gaps in GAW networks and projects." It is the mission of GALION to organize such observational capability for the 4-dimensional distribution of key aerosol parameters.

Background Literature:

GAW (2003) WMO/GAW Aerosol Measurement procedures guidelines and recommendations (GAW Report 153)

GAW (2004) The Integrated Global Atmospheric Chemistry Observations (IGACO) Report of IGOS-WMO-ESA (September 2004) (GAW Report 159)

GAW (2005) WMO/GAW Experts Workshop on a Global Surface-based Network for Long Term Observations of Column Aerosol Optical Properties (Davos, Switzerland, 8-10 March 2004) (GAW Report 162) , 152 pp, November 2005.

GAW (2007) WMO Global Atmosphere Watch (GAW) Strategic Plan: 2008 - 2015 (GAW Report 172

GAW (2008) Plan for the implementation of the GAW Aerosol Lidar Observation Network GALION (Hamburg, Germany, 27-29 March 2007) (WMO TD No. 1443, GAW Report 178), 52 pgs, November 2008.

Posted by Nikisa Jordan at 11:10 AM